1. Field of the Invention
The present invention relates to a pinned photodiode sensor with gate-controlled silicon-controlled rectifier (SCR) transfer switch, and more particularly, to a gate-controlled SCR transfer switch with a gate having different doped regions.
2. Description of the Prior Art
In the prior art, there is a process of integrating a pinned photodiode into an active pixel sensor. Please refer to FIG. 1, which is a diagram of a pinned photodiode integrated into an active pixel sensor according to the prior art. There are a P+ doped region 12, an N− doped region 14, an N+ doped region 16, an oxide layer 17, and a gate 18 formed on a P-type substrate 10. The process related to the structure of FIG. 1 has advantages of better blue response, and low dark current.
Since there are plenty of interface traps between the oxide layer 17 and the substrate 10, such interface traps release or capture electrons or holes with changes of temperature or electric field intensity, resulting in dark current leakage. When the oxide layer 17 contacts the P+ doped region 12, the P-type substrate 10, or the N− doped region 14, the region contacting the oxide layer 17 can provide electrons or holes to prevent a depletion region from touching interface traps of surface interfaces to generate dark current. However, the structure of FIG. 1 cannot completely prevent dark current leakage during operation.
Please refer to FIG. 2, which is a diagram of entering an exposure procedure after resetting the pinned photodiode of FIG. 1. When resetting the pinned photodiode, the gate 18 is connected to a high voltage so as to generate a depletion region 13 (between dotted line 5 and dotted line 7) between the P-type substrate 10 and the N− doped region 14 and a depletion region 19 (between dotted line 7 and dotted line 9) between the P+ doped region 12 and the N− doped region 14. The depletion regions 13 and 19 reach the interfaces (shown as a circle 15 in FIG. 2), and interface traps might release or capture electrons or holes, leading to dark current leakage and noise when the active pixel sensor captures images.